1. Technical Field
The invention relates to interactive displays. More particularly, the invention relates to a method and apparatus for determining user gestures to control a touch detecting, interactive display.
2. Description of the Prior Art
There are many situations in which one or more individuals interactively explore image-based data. For example, a team of paleontologists may wish to discuss an excavation plan for a remote dig site. To do so, they wish to explore in detail the geographic characteristics of the site as represented on digitized maps. In most laboratories, this requires the team either to huddle around a single workstation and view maps and images on a small display, or sit at separate workstations and converse by phone. The activity of exploring imagery is much more easily and effectively accomplished with the users surrounding a single large display. A particularly effective approach is a touch detecting, interactive display such as that disclosed in the related patent application entitled Touch Detecting Interactive Display, filed Aug. 6, 2004, Ser. No. 10/913,105. In such a system, an image is produced on a touch detecting display surface. A touch sensor determines the locations at which a user contacts the display surface, and based on the position and motions of these locations, user gestures are determined. The display is then updated based on the determined user gestures.
A wide variety of mechanisms are available for determining the locations at which a user contacts the touch sensor. Often, a grid-based approach is used in which measurements acquired on the perimeter of the touch sensor indicate a horizontal coordinate x1 and a vertical coordinate y1 for each contact location.
FIG. 1 shows is a schematic diagram that shows a prior art infrared break-beam, grid-based touch sensor for determining the coordinates of two contact locations. The approach shown is similar to that disclosed in U.S. Pat. No. 3,478,220 to Milroy, U.S. Pat. No. 3,764,813 to Clement et al., U.S. Pat. No. 3,775,560 to Ebeling et al., and U.S. Pat. No. 3,860,754 to Johnson et al. These systems incorporate a series of horizontal and vertical beams generated by infrared LED's and a corresponding series of infrared sensors. In FIG. 1, a point of contact C1 interrupts the beam of light passing from an emitter E1x to a sensor S1x and the beam of light passing from an emitter E1y to a sensor S1y. A similar interruption of beams is created by a contact point C2. The locations of the contact points (x1,y1) and (x2,y2) are determined by considering the x and y locations of the interrupted beams. A well known shortcoming of this approach to determining contact locations is a ghosting effect in which the pair of contact locations C1 and C2 cannot be distinguished from the pair of contact locations C1′ and C2′. Accordingly, the contact information returned by grid-based touch sensor is best considered as a bounding box defined by the rectangle C1C1′C2C2′.
This method of determining and reporting the locations of contacts differentiates grid-based sensors from many other touch sensor technologies such as the Synaptics TouchPad™ found on many laptop computers. By measuring changes in capacitance near a wire mesh, the TouchPad™ determines contact positions directly and reports an absolute position to the host device. Clearly, an ability to directly ascertain and report the position of a contact is in many situations advantageous. However, capacitive sensors do not scale well, and are therefore impractical or prohibitively expensive for incorporation into large interactive displays.
A number of methods have been proposed for recognizing user gestures through tracking the position and motion of one or more contact locations determined by a touch sensor. Clearly, these methods encounter difficulty when used in conjunction with a grid-based sensor that cannot disambiguate the location of multiple simultaneous contact points. It would thus be advantageous to define a set of user gestures in terms of the bounding box surrounding the detected contact locations. Such a set of user gestures would permit the use of inexpensive, highly reliable, and highly scalable grid-based touch sensors yet still allow users to interact with the display in an intuitive manner.